1. Field of the Invention
The present invention relates to a magnetic steering angle detection apparatus for detecting a steering angle of a vehicle steering, and particularly, to a technology for reducing an influence from an external magnet.
2. Description of the Related Art
As a conventional example of a steering angle detection apparatus mounted on a vehicle, one described in a Japanese Patent Translation Publication No. Hei 11-500828 (published in 1999) is known. In this document, as shown in FIG. 1, the steering angle detection apparatus 102 is mounted in the column cover 101. The steering angle detection apparatus 102 detects the rotation angle of the angle detection magnet 105 rotating in synchronization with the steering shaft 103 by means of the anisotropic magnetoresistive element (hereinafter, referred to as AMR) 104, thus computing the rotation angle of the steering shaft 103.
In this case, the AMR 104 is configured to detect the rotation angle of the angle detection magnet 105 by sensing a magnetic field in a direction orthogonal to the steering shaft 103, that is, in a direction shown by the arrow Y101.
At this time, when a driver carries the magnet (magnetized object) 106 to the inside of the vehicle and places the magnet 106 close to the column cover 101, a magnetic field is sometimes generated in the direction orthogonal to the steering shaft 103 (direction of the arrow Y101). By this magnetic field, a misdetection of a measured angle by the AMR 104 occurs in some case. In such a case, this misdetection results in a miscomputation of the steering angle.
For example, a steering angle detection apparatus, which is configured such that a keyholder fixing magnet is mounted on the side face of a column switch, is affected by this fixing magnet, and consequently, a measure for shielding the apparatus from the external magnetic field becomes required. Although a method of providing a magnetic shield can be considered to be a measure for shielding the apparatus from the external magnetic field, the use of this method increases the number of parts, thus causing the problem of increase in size and cost of the apparatus.